RokAccess is a simple content mambot that allows you show certain portions of a content item to any Joomla! group.

Access Plugin (ACL) One or more group name should be adopted, you can explicitly deny access by putting an "!" Before the group name / user in question. It execute loop list provided law until it finds a "correct" (there are sometimes strange results occur with groups of access). The standard Joomla! Hierarchy also applies. Valid group names are: - guest - registered - author - editor - publisher - manager - administrator - super administrator - special (administrator or super administrator) But in addition, - the group component / hack gmaccess access to manage rights to the product, component, menu module, etc. Download and install Component "GMAccess" available on http://www.joomlafrance.org/telecharger/fileinfo/GMAccess.html Usage: {rg_access [!]group[,group]}...some content...{/rg_access} Examples: {rg_access guest}shows only to guest users{/rg_access} {rg_access !guest}shows to all users who are not a guest{/rg_access} {rg_access registered}shows to all users who are registered{/rg_access} {rg_access guest,!editor}shows to all guests and members who are NOT editors{/rg_access} {rg_access editor,special}shows to editors, administrators, and superadministrators{/rg_access} {rg_access group_gmaccess}shows to group_gmaccess{/rg_access} {rg_access user_gmaccess}shows to user_gmaccess{/rg_access} 

This extension for J! 1.5 is a maintenance utility that allows you to manipulate the Access Control tables provided with Joomla!
Features
• Builds on the existing phpGACL API used within Joomla!
• Adds the extra tables required to use the full phpGACL API
• Add your own User Groups (more than just Registered, Author, Editor, etc)
• Add your own Access Levels (more than Public, Registered, Special, etc)
• Create your own Permissions
• Create your own Rules by binding permissions to User Groups and Access Levels
• 100% Open Source - released under the GNU General Public License
The JXtended Libraries plugin is required. 

JUGA is a Joomla Extension that allows additional control over what content is available to which users.

As you probably know, Joomla 1.5 doesn't allow a granular Access Control, but an ACL will probably be a feature of new Joomla! versions (1.6?). In the meantime, I decided to write this simple extension. This totally unobtrusive plugin allows you to introduce some basic Access Control in your Joomla! extensions (components and modules), without having to edit the Joomla! core files or the Joomla! core database. If you need to categorize your users in groups (let say, students and teachers), giving them specific permissions in the front-end and/or different views of your Joomla! website, this Joomla! plugin is what you need.

An ACL Enhancements component for Joomla! to enable you to create new user groups and/or new access levels.
It also enables you to assign multiple access levels to user group to make your website items' view access more controllable.
 

GroupJive is a Group social networking component enabling users to create Groups with other users.

This components allows you to give individual users access to certain menu items.

This simple graphical interface makes the use of the Joomla! Access Control Plugin easier. With this plugin you can use the administration panel to create/delete groups, to associate users to one or more groups and to manage user permissions.
You need to install Joomla! Access Control Plugin and this component to make the Access Control mechanism working on your platform.